1. Field of the Invention
The present invention relates to a startup controller for an in-cylinder injection internal combustion engine having a function of promptly increasing fuel pressure at a startup.
2. Description of Related Art
An in-cylinder injection engine, which injects fuel directly into a cylinder, takes a short time from injection to combustion compared to an intake port injection engine, which injects fuel into an intake port. The in-cylinder injection engine does not have enough time to atomize the injected fuel. Therefore, the in-cylinder injection engine has to elevate injection pressure to atomize the injected fuel. The in-cylinder injection engine is so constructed that fuel pumped up from a fuel tank by a low-pressure pump is pressurized and pressure-fed to a fuel injection valve by a high-pressure pump driven by a camshaft of the engine.
During stoppage of the engine, the high-pressure pump and low-pressure pump are also stopped and therefore fuel pressure in a fuel pipe decreases with time. Therefore, a prolonged engine stoppage causes the fuel pressure to be decreased to substantially 0 MPa. At startup, it takes a certain time for the fuel pressure to increase to a high fuel-pressure range suitable for the startup. Accordingly, the fuel is injected at a low fuel pressure at the startup, insufficiently atomizing the injected fuel. In this case, a combustion quality can be degraded or in-cylinder wet can increase, resulting in worsened startup properties and deteriorated exhaust emissions at the startup.
As a countermeasure against such problems, startup control for an in-cylinder injection engine described in JP-A-H11-270385 is arranged to stop injection for a predetermined period in an initial stage of the startup and to increase fuel pressure to a high fuel-pressure range suitable for the startup during the period of injection stoppage with the use of a high-pressure pump. Then, the control starts the injection.
With this startup control for the in-cylinder injection engine, however, the fuel injection is stopped at the startup until the fuel pressure is increased by the high-pressure pump to a high fuel-pressure range suitable for the startup. This causes problems of a prolonged startup time and an increased amount of emissions of in-cylinder residual gas including unburned hydrocarbon (HC).
The fuel-pressure increasing time at the startup can be shorted by increasing the size of the high-pressure pump or decreasing the volume of a high-pressure fuel pipe or delivery pipe. However, an increased high-pressure pump size brings about problems such as worsening of mountability into a vehicle, deterioration of fuel pressure controllability in a low-discharge range and an increase in fuel pressure pulsation.